The present invention relates to a micro-mirror device that is configured to scan light and a driving mechanism that is incorporated in the micro-mirror device.
Conventionally, an electrostatic capacity type micro-mirror (hereinafter, simply referred to as a micro-mirror) is used in various technological fields such as an optical switch for telecommunication, a measuring instrument, and a scanner. The micro-mirror device is provided with a driving mechanism that is located on the opposite side of a mirror surface scanning incident light. The mirror-device is designed such that the mirror surface is tilted by electrostatic attractive force which is generated by applying voltage to the driving mechanism. Recently, the micro-mirror device is required to be more downsized while generating greater electrostatic attractive force for tilting the mirror surface. An example of a micro-mirror device that meets such requirements is disclosed in Japanese Patent Provisional Publications No. P2000-147419.
A micro-mirror device disclosed in this publication (JP P2000-147419) is provided with movable comb electrodes and fixed comb electrodes on the opposite side of a mirror surface, which engage with each other. To be more concrete, there are provided two pairs of a movable comb electrode and a fixed comb electrode that face each other across a turning axis on the opposite side of the mirror surface. The structure of the device disclosed in this publication enables to downsize the entire device.
However, if a micro-mirror device is designed as disclosed in this publication (JP P2000-14179), there is a problem that a mirror surface may be translated in a vertical direction (a direction perpendicular to the mirror surface) by electrostatic attractive force generated by a bias voltage that is previously applied to fixed electrodes. If the mirror surface is translated, misalignment of a light incident point on the mirror surface will occur. Such misalignment results in a problem that light incident on the mirror surface scans an area out of a predetermined scanning area Further, the translation of the mirror surface could cause a so-called pull-in phenomenon and/or a phenomenon in which undue stress is applied to a hinge that rotatable supports the mirror, thereby damaging inside the device.